Research Of Low-voltage Ride Through Technology Of Direct Drive Wind Power System

In recent years the energy crisis and environmental pollution have become two major bottlenecks restricting the development of human society.Wind power,represented as a clean renewable energy generation,has got more favor of people.It is necessary to study the grid connected operation of wind power system.However interconnection brings many problems,especially the safety and stability problems of the system.LVRT technology ensures that the wind turbines keep non-stop running,even provides a certain amount of reactive power to the grid until the network back to normal.The direct drive wind power system,compared with traditional one,is currently one of the most promising wind power system.A direct-drive permanent magnet synchronous generator,without the gear box,is more flexible when controls reactive power and is more advantageous in realizing LVRT operation.This article studies the LVRT technology of direct drive wind power system.It includes two aspects.First,the Crowbar circuit is put forward to implement the power balance of machine side converter and web side converter,also eliminate the over voltage of dc side.Then provide a new reactive power control strategy,simulation verify the effectiveness of the control strategy.Secondly,as to the dc voltage stability control of the asymmetry of direct drive wind power system,in order to stabilize dc bus voltage,a new type of control strategy called PN-VOC which added the energy release circuit in DC side has been discussed.